Destruction of cellular tissues in situ has been used in the treatment of diseases and medical conditions alone or as an adjunct to surgical removal procedures. These methods are often less traumatic than surgical procedures and may be the only alternative where surgical procedures are unfeasible. Phototherapeutic treatment devices, e.g., lasers, have the advantage of using intense light energy which is rapidly attenuated to a non-destructive level outside of the target region. However, blood and/or other body fluids greatly diminish the effectiveness of several of these light energy sources as the radiation passes from an energy source, e.g., a laser source, through the body fluid to a treatment site. For example, the energy can be scattered or be absorbed by blood and other body fluids between the energy source and the tissue treatment site.
A common medical application of lasers is in the irradiation of tissue, both internal and external. For external treatment, the laser energy can be applied directly. However, where a procedure requires irradiation of internal tissues that are not readily accessible to external energy sources, the use of catheter-type devices to deliver coherent radiation to the treatment site is common. Typical applications requiring use of laser catheters are found in the treatment of various anatomical structures and conditions within the cardiovascular system.
Microwave, radio frequency, and acoustical (ultrasound) devices as well tissue destructive substances have also been used to destroy malignant, benign and other types of aberrant cells in tissues from a wide variety of anatomical sites and organs. Tissues sought to be treated include isolated carcinoma masses and, more specifically, organs such as the prostate, bronchial passage ways, passage ways to the bladder, passage ways to the urethra, and various passage ways into the thoracic area, e.g., the heart.
Devices useful for the treatment of such disease states or conditions typically include a catheter or a cannula which can be used to carry an energy source or waveguide through a lumen to the zone of treatment. The energy is then emitted from the catheter into the surrounding tissue thereby destroying the diseased tissue, and sometimes surrounding tissue.
Catheters have been utilized in the medical industry for many years. One of the greatest challenges in using a catheter is controlling the position and placement of the distal portion of the catheter from a remote location outside of the subject's body. Some catheters have features designed to aid in steering the catheter and overcoming this challenge. However, several significant problems are still encountered with catheters.
Careful and precise control over the catheter is required during critical procedures which ablate tissue within the heart. Such procedures are termed “electrophysiological” therapy and are becoming widespread for treatment of cardiac rhythm disturbances. During these procedures, an operator guides a catheter through a main artery or vein into the interior of the heart which is to be treated. The operator manipulates a mechanism to cause an electrode which is carried on the distal tip of the catheter into direct contact with the tissue area to be treated. Energy is applied from the electrode into the tissue and through an indifferent electrode (in a uni-polar electrode system) or to an adjacent electrode (in a bi-polar electrode system) to ablate the tissue and form a lesion. The irradiation of tissue must be accomplished with great precision as the danger of also damaging other adjacent tissue is always present, especially when the process occurs remotely at the distal end of a relatively long catheter.
One partial solution to this problem has been to “map” the area to be treated prior to a procedure. Cardiac mapping can be used prior to ablation to locate aberrant conductive pathways within the heart. The aberrant conductive pathways are called arrhythmias. Mapping of the heart identifies regions along these pathways, termed “foci”, which are then ablated to treat the arrhythmias.
During laser ablation procedures, a catheter serves to deliver a fiber optic wave guide to the target region. Radiation transmitted through the optical fiber essentially vaporizes the targeted tissue to achieve the desired therapeutic goals of the procedure. Complete destruction of target tissue, with the exception of certain narrow and specific cardiac treatments, is generally limited to cardiological applications, e.g., removal of a blockage. In electrophysiological treatments, total destruction of target tissue (ablation) is not necessary, but controlled denaturation of tissue to affect its electrophysiological properties is required.
Within the heart, variations in cardiac tissue characteristics, perhaps as the result of scarring from previous cardiac trauma, can present vastly different tissue that react differently to the laser energy source. For example, absorption characteristics of normal tissue can be much different from tissue that is heavily scarred. In addition, the trabecular nature of the endocardium increases the difficulty because the laser radiation must reach a highly contoured or folded target tissue surface. As a result, temperatures of the tissue surface where the laser energy is incident can be much higher for some tissue than for others. In the treatment of cardiac tissue, the dynamic state of the heart tissue further complicates the situation in that the heart is constantly moving during treatment. Thus, incorporation of fixation means to maintain the position of the distal end of the laser catheter with respect to the target tissue site is often required.
There are drawbacks with many of the currently available catheters and treatments. Oftentimes it is difficult, if not impossible, to maneuver the instrument into small passage ways, such as a ventricle, without damaging the surrounding tissue. Most therapeutic treatments require that the apparatus is in contact with the tissue and with blood and/or other body fluids. Additionally, focusing the ablative energy onto the tissue site to be treated can be problematic, especially when vital organs surround the diseased tissue. Therefore, it would be desirable to focus ablative energy onto a specific treatment area wherein surrounding tissue is not degraded, the energy source is not in direct contact with the tissue and blood and body fluids are not coagulated or destroyed.